1. Field of the Invention
The present invention relates to a base unit and a disk drive apparatus.
2. Description of the Related Art
A known base plate for use in a disk drive apparatus is described in JP-A 2008-027540. This base plate is defined by a substantially plate-shaped member made of a metal, and includes a first surface including a recessed portion in which a disk-shaped recording medium (i.e., a hard disk), a motor, a magnetic head, and an actuator therefor are accommodated, and a second surface to which a control circuit board is fixed. A resin coating layer is defined on a surface of the base plate through electrocoating.
The base plate includes a sealing surface to be tightly covered with a cover plate, and arranged around the recessed portion, that is, along four sides of the base plate, which is substantially rectangular in a plan view, and screw holes used for screwing the cover plate are defined in the base plate at four corners and at two substantially middle positions along long sides. Fixing screws are screwed into the screw holes with a seal member (e.g., a rubber packing) being held between the sealing surface of the base plate and the cover plate. As a result, the recessed portion defined in the first surface of the base plate defines an enclosed space surrounded by the base plate and the cover plate.
The resin coating layer is defined on the above-described known base plate. Resins are generally more hygroscopic than metals. Accordingly, moisture outside of the enclosed space surrounded by the base plate and the cover plate may be absorbed by the resin coating layer and travel through the resin coating layer to enter into the enclosed space. Therefore, the moisture, entering into the enclosed space, may be attached to the disk-shaped recording medium, the magnetic head, or the like, which may result in reduced reliability of the base plate.